A new aircraft surveillance system being rolled out at select mountain airports in Colorado promises to boost the capacity and efficiency of takeoffs and landings at airfields surrounded by rugged, often deadly, terrain.

And it aims to increase aircraft flow rates without compromising safety.

On Sept. 12, air-traffic controllers started using the system for flights in and out of Craig, Steamboat Springs, Hayden and Rifle.

They are among the first airports in the country to use technology called Wide Area Multilateration, or WAM, which allows controllers to “see” planes for the first time on radar displays when the aircraft are arriving and departing at airfields framed by high terrain.

Controllers at the Federal Aviation Administration’s Air Route Traffic Control Center in Longmont handle air traffic for most airports on the Western Slope.

WAM aims to boost the flow of traffic into mountain airports, especially during ski season, when a significant increase in the number of flights often is coupled with bad weather, said Travis Vallin, aeronautics director for the Colorado Department of Transportation.

In the past, the combination of high traffic volume and inclement weather has led to flight delays and other inefficiencies.

CDOT spent five years and about $5.7 million bringing WAM technology to the mountain airports. The state agency turned the system over to the FAA to operate.

Before the introduction of WAM, controllers could rely only on traditional radar to track planes flying in and out of mountain airports.

Adding time for safety

Because radar has a line-of- sight requirement between the ground antenna and plane, controllers often lose radar coverage for planes flying into many mountain airports, especially when the aircraft get below 9,000 feet.

When radar coverage is lost, controllers have to slow the flow of mountain air traffic, with as much as 10-minute separations between flights under some circumstances, said Greg Dyer, the FAA’s support manager for airspace and procedures at the Longmont air-traffic facility.

At airports without WAM, pilots follow published arrival procedures when traditional radar coverage is lost, and then report when they have landed so controllers can position a plane for takeoff and offer instructions for the next arriving aircraft.

Experts refer to this often inefficient technique as “one in/one out.”

The new system takes over from traditional radar in mountain valleys by using an array of ground sensors, strategically placed around the airports, to take signals from plane transponders and triangulate the plane’s position to create a radar target on controller screens at low altitudes and all the way to the ground.

WAM should allow for more efficient sequencing of arriving and departing aircraft and help avoid fuel-wasting and time-consuming circling maneuvers that controllers often put planes in when high traffic volumes, bad weather and the loss of radar coverage combine.

The WAM sensors are the size of a refrigerator and cost about $250,000 apiece, Vallin said. CDOT and FAA have installed 20 of the units at the four airports outfitted so far.

In comparison, the installation and maintenance of a conventional radar unit can cost about $10 million, Dyer said.

Sitting at a radar display at the Longmont facility last week, controller John Tutor watched as a plane approached the Yampa Valley airport at Hayden.

“On the ILS (instrument landing system), we will be able to see planes lower and should see them all the way in to the runway,” Tutor said of the new system. “It will be a quantum improvement at Hayden.”

Before the introduction of WAM, controllers would not have radar targets for planes operating in an area up to about 4,000 feet above Hayden, said the 48-year-old Tutor, a controller for 24 years.

Expanding to 7 airports

FAA and CDOT hope to add WAM to seven other airfields on the Western Slope — Alamosa, Aspen, Cortez, Durango, Gunnison, Montrose and Telluride — in a second-phase installation.

WAM has a side benefit of assisting in aviation search and rescue, Vallin said.

That was demonstrated in December when a small Piper airplane crashed while approaching the Yampa Valley airport during a WAM test phase.

But after the crash was reported minutes later, FAA personnel pulled the raw WAM test data showing the track of the plane after the loss of the conventional radar signal.

The WAM data allowed controllers to give far more precise information to search and rescue personnel on the likely crash site, said Joe Ashworth, an FAA quality control specialist in Longmont.

Both occupants of the Piper were killed, so using WAM to pinpoint the accident site and speed search and rescue may not have mattered in this incident.

But Vallin said of the new technology: “I’m convinced this will save lives someday.”

Jeffrey Leib: 303-954-1645 or jleib@denverpost.com

Handling rush of skiers

A computer screen shows all arrivals and departures on a winter day at Colorado airports near ski areas. The new airplane surveillance system will help air-traffic controllers follow planes descending in mountain areas and should speed airport takeoffs and landings to avoid flight delays.

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